In which year did the British Empire reach its greatest territorial extent? The answer is 1922. The empire reached its maximum postwar size after the First World War, when Britain received former German and Ottoman territories as League of Nations mandates.
These additions included Tanganyika, mandated to Britain after Germany lost its colonies, as well as mandates in the Middle East such as Iraq and Palestine. Together with long-established possessions in India, Africa, the Caribbean, Southeast Asia, the Pacific, and the Dominions, the empire covered roughly 35 million square kilometres—more than a quarter of the world’s land area.
Some references place the precise territorial peak around 1920, when the postwar settlement was being formalised, but 1922 is the conventional quiz answer because the mandates and new imperial arrangements had become established by then. This was a geographic high point, not a sign of unlimited strength: Britain was financially strained after the war, nationalist movements were growing, and decolonisation had already begun.